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United States Patent |
5,223,881
|
Nakagawa
,   et al.
|
June 29, 1993
|
Apparatus for controlling developing solution
Abstract
An alkaline developing solution is used in development of photosensitive
organic resin (photoresist) in liquid crystal board manufacturing process
or printed board manufacturing process. The apparatus for controlling
developing solution comprises developing solution discharge device for
discharging developing solution by detecting the dissolved resin
concentration in the developing solution by means of an absorption
photometer (16), first replenishing device for replenishing undiluted
developing solution and pure water by detecting the liquid level of the
developing solution by means of a liquid level gauge (3), and second
replenishing device for replenishing undiluted developing solution or pure
water by detecting the alkali concentration of the developing solution by
an electric conductivity meter (15). By thus constituting, the developing
performance of the developing solution may be always kept constant, and
the operation down time may be notably shortened.
Inventors:
|
Nakagawa; Toshimoto (Kawasakishi, JP);
Tsukada; Kouzo (Yokohamashi, JP);
Ogawa; Shu (Nagareyamashi, JP);
Shiotsu; Shinichiro (Tatsunoshi, JP)
|
Assignee:
|
Hirama Rika Kenkyujio Ltd. (both of, JP);
Nagase & Co., Ltd. (both of, JP)
|
Appl. No.:
|
907665 |
Filed:
|
July 2, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
396/570; 396/627 |
Intern'l Class: |
G03D 003/02 |
Field of Search: |
354/298,299,316,320,321-324
134/64 P,122 P
|
References Cited
U.S. Patent Documents
5121164 | Jun., 1992 | Landa et al. | 355/246.
|
5168296 | Dec., 1992 | Nakamura et al. | 354/320.
|
Primary Examiner: Rutledge; D.
Attorney, Agent or Firm: Jones, Tullar & Cooper
Claims
What is claimed is:
1. An apparatus for controlling developing solution comprising developing
solution discharge means for discharging developing solution by detecting
the dissolved resin concentration in the developing solution for
photosensitive organic resin by means of an absorption photometer, first
replenishing means for replenishing undiluted developing solution and pure
water by detecting the liquid level of the developing solution by means of
a liquid level gauge, and second replenishing means for replenishing
undiluted developing solution or pure water by detecting the alkali
concentration of the developing solution by means of an electric
conductivity meter.
2. An apparatus for controlling developing solution comprising developing
solution discharge means for discharging developing solution by detecting
the dissolved resin concentration in the developing solution for
photosensitive organic resin by means of an absorption photometer, first
replenishing means for replenishing a fresh developing solution
preliminarily blending undiluted developing solution and pure water by
detecting the liquid level of the developing solution by means of a liquid
level gauge, and second replenishing means for replenishing undiluted
developing solution or pure water by detecting the alkali concentration of
the developing solution by means of an electric conductivity meter.
3. An apparatus for controlling developing solution comprising third
replenishing means for replenishing undiluted developing solution and pure
water by detecting the dissolved resin concentration in the developing
solution for photosensitive organic resin by means of an absorption
photometer, and second replenishing means for replenishing undiluted
developing solution or pure water by detecting the alkali concentration of
the developing solution by means of an electric conductivity meter.
4. An apparatus for controlling developing solution comprising third
replenishing means for replenishing a fresh developing solution
preliminarily blending undiluted developing solution and pure water by
detecting the dissolved resin concentration in the developing solution for
photosensitive organic resin by means of an absorption photometer, and
second replenishing means for replenishing undiluted developing solution
or pure water by detecting the alkali concentration of the developing
solution by means of an electric conductivity meter.
Description
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for controlling alkaline developing
solution used in developing photosensitive organic resin (photoresist,
hereinafter called simply resin) in liquid crystal board manufacturing
process, printed board manufacturing process or the like, and more
particularly to an apparatus combining a continuous automatic replenishing
mechanism in cyclic use of alkaline developing solution, an alkali
concentration regulating mechanism, and a developing solution automatic
discharge mechanism for arresting deterioration of developing performance
due to enrichment of dissolved resin.
In liquid crystal board manufacturing process or printed board
manufacturing process, an alkaline aqueous solution, such as tetramethyl
ammonium hydroxide (TMAH) aqueous solution (for example, 2.380 wt. %) and
potassium hydroxide aqueous solution, is used as a developing solution of
resin in spray method or dip method.
In the conventional method, starting by filling a development processing
tank with the specified volume of a fresh developing solution at the
specified concentration, when the developing solution is consumed and
reaches a specified deterioration concentration region, on the basis of an
empirical index such as the number of boards processed, the whole volume
is exchanged with a prepared fresh solution in the batch operation system.
This solution exchanging frequency varies with the type of the boards, but
it is generally done once in every about six hours.
An alkaline aqueous solution used as the developing solution of resin
gradually lowers in the alkali concentration in the course of use due to
reaction with acid in the resin, and absorption and reaction of carbon
dioxide and oxygen gas in the air, and the effective sensitivity declines
sequentially, but, hitherto, the alkali concentration was not measured in
real time and controlled at the specified concentration.
Besides, the resin dissolved in the developing solution in the development
processing is gradually enriched, and in the positive resist, it functions
to slightly dissolve the resin in the unexposed area that should not be
dissolved, and the residual film rate of the unexposed part is gradually
lowered, but conventionally the resin concentration was not measured in
real time and controlled at the specified concentration.
Therefore, in this period, the alkali concentration and the dissolved resin
concentration vary with the passing of the time and are not constant, and
it was hence difficult to control the delicate dimensional precision in
developing the boards, the product quality was unstable, and the yield was
lowered.
Besides, due to stopping of operation (down time) for exchanging solution,
the operation rate was significantly lowered, and the exchange work of the
developing solution required an extra labor cost.
Moreover, since the developing solution was adjusted to the specified
concentration and the specified quality, and shipped in an enclosed
container free from contamination with foreign matter, the transportation
cost was enormous, and as compared with the undiluted developing solution,
the material cost was much higher.
OBJECTS AND SUMMARY OF THE INVENTION
It is hence a primary object of the invention to solve the above-discussed
problems of the prior art, while maintaining the advantages of the
convenient line conveying system of the prior art suited to mass
production in the liquid crystal board manufacturing process, printed
board manufacturing process, and the like.
In other words, it is an object of the invention to control automatically
the developing solution to the specified alkali concentration and the
dissolved resin concentration upon receiving the undiluted developing
solution at the using side of the developing solution, control adequately
the solution replenishment in the development processing tank so as to
keep always constant the developing solution, shorten the operation
stopping time markedly, and reduce the comprehensive manufacturing cost.
The invention is intended to adjust and control the resin concentration by
measuring the absorbance by experimentally confirming that the
concentration of the resin dissolved in the developing solution in the
development processing tank is closely related with its absorbance, and to
adjust and control the alkali concentration by measuring the electric
conductivity by experimentally confirming that the alkali concentration in
the developing solution is closely related with its electric conductivity.
To achieve the above objects, the invention presents an apparatus for
controlling developing solution which comprises developing solution
discharge means for discharging the developing solution by detecting the
dissolved resin concentration in the developing solution for
photosensitive organic resin by means of an absorption photometer, first
replenishing means for replenishing undiluted developing solution and pure
water by detecting the liquid level of the developing solution by a liquid
level gauge, and second replenishing means for replenishing undiluted
developing solution or pure water by detecting the alkali concentration of
the developing solution by means of an electric conductivity meter.
In the apparatus for controlling developing solution of the invention, the
first replenishing means replenishes, instead of replenishing undiluted
developing solution and pure water, a diluted developing solution
preliminarily blending the undiluted developing solution and pure water.
The apparatus for controlling developing solution of the invention further
comprises third replenishing means for replenishing undiluted developing
solution and pure water by detecting the dissolved resin concentration in
the developing solution for photosensitive organic resin by means of an
absorption photometer, and second replenishing means for replenishing
undiluted developing solution or pure water by detecting the alkali
concentration of the developing solution by means of an electric
conductivity meter.
In the apparatus for controlling developing solution of the invention, the
third replenishing means for replenishing by detecting the dissolved resin
concentration in the developing solution for the resin by means of an
absorption photometer replenishes, instead of replenishing undiluted
developing solution and pure water, a diluted developing solution
preliminarily blending the undiluted developing solution and pure water.
Examples to be used as the undiluted developing solution include, among
others, an inorganic alkaline aqueous solution composed of a single
inorganic alkali such as potassium hydroxide, sodium hydroxide, sodium
phosphate and sodium silicate or their mixture, and an organic alkaline
aqueous solution such as tetramethyl ammonium hydroxide (TMAH) and
trimethyl monoethanol ammonium hydroxide (choline).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an apparatus for controlling developing
solution showing an embodiment of the invention.
FIG. 2 is a schematic diagram of an apparatus for controlling developing
solution showing other embodiment of the invention.
FIG. 3 is a schematic diagram of an apparatus for controlling developing
solution showing a different embodiment of the invention.
FIG. 4 is a schematic diagram of an apparatus for controlling developing
solution showing a further different embodiment of the invention.
FIG. 5 is a graph of an operation example showing the relation between the
alkali concentration and the line width of resin after development.
FIG. 6 is a graph of an embodiment showing the relation between the
electric conductivity and the alkali concentration relating to the
invention.
FIG. 7 is a graph of an operation example showing the relation between the
dissolved resin concentration and the residual film rate in unexposed
area.
FIG. 8 is a graph of an embodiment showing the relation between the
absorbance and the dissolved resin concentration relating to the
invention.
FIG. 9 is a graph showing the relation between the alkali concentration and
the time when the apparatus of the invention is used.
FIG. 10 is a graph showing the relation between the alkali concentration
and the time in the conventional method.
FIG. 11 is a graph showing the relation between the dissolved resin
concentration and the time when the apparatus of the invention is used.
FIG. 12 is a graph showing the relation between the dissolved resin
concentration and the time in the conventional method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, some of the preferred embodiments of the
invention are described in detail below.
As shown in FIG. 1, the invention presents an apparatus for controlling
developing solution which comprises developing solution discharge means
for discharging the developing solution by detecting the dissolved resin
concentration in the developing solution for photosensitive organic resin
by means of an absorption photometer 16, first replenishing means for
replenishing undiluted developing solution and pure water by detecting the
liquid level of the developing solution by a liquid level gauge 3, and
second replenishing means for replenishing undiluted developing solution
or pure water by detecting the alkali concentration of the developing
solution by means of an electric conductivity meter 15.
In the apparatus for controlling developing solution of the invention, the
first replenishing means replenishes, as shown in FIG. 2, instead of
replenishing undiluted developing solution and pure water, a diluted
developing solution preliminarily blending the undiluted developing
solution and pure water.
The apparatus for controlling developing solution of the invention further
comprises, as shown in FIG. 3, third replenishing means for replenishing
undiluted developing solution and pure water by detecting the dissolved
resin concentration in the developing solution for photosensitive organic
resin by means of an absorption photometer 16, and second replenishing
means for replenishing undiluted developing solution or pure water by
detecting the alkali concentration of the developing solution by means of
an electric conductivity meter 15.
In the apparatus for controlling developing solution of the invention, as
shown in FIG. 4, the third replenishing means for replenishing by
detecting the dissolved resin concentration in the developing solution for
the resin by means of an absorption photometer 16 replenishes, instead of
replenishing undiluted developing solution and pure water, a diluted
developing solution preliminarily blending the undiluted developing
solution and pure water.
FIG. 1 is a schematic diagram of an apparatus showing an embodiment of the
invention. In the diagram, reference numbers 1 to 13 correspond to the
units for composing the conventional development processing apparatus.
That is, the conventional development processing apparatus comprises a
development processing tank 1 for storing the developing solution, an
overflow tank 2, a liquid level gauge 3, a development compartment hood 4,
a developing solution spray 7, a liquid feed pump 8 for feeding the
solution to the developing solution spray, a filter 9 for removing fine
particles from the developing solution, roller conveyors 5 moving while
developing with a board mounted on, boards 6, a circulation pump 11 for
clarifying and agitating developing solution, a filter 13 for removing
fine particles, and pipings for N.sub.2, pure water, etc.
According to the invention, the devices attached to the development
processng apparatus include an electric conductivity meter 15, absorption
photometer 16, liquid discharge pump 18, undiluted developing solution
feed tank 19, flow rate regulating valve 21 for feeding undiluted
developing solution, flow rate regulating valve 22 for feeding pure water,
pipings for connecting these devices, electric instrumentations or
pneumatic instrumentations.
The liquid volume stored in the development processing tank 1 is sufficient
if enough to feed the required volume for the developing solution spray 7,
but it must be controlled for the stability of the process. The liquid
level gauge 3 detects liquid level drop due to spontaneous decrease as the
solution adhesion on the board and is brought outside during development
process, or detects liquid level drop when the solution deteriorating in
development performance is discharged by force, and controls the liquid
volume in the development processing tank 1 in a specific range. Here, the
old solution is passed into the drain piping by operating the discharge
pump 18. Or the old solution may be directly discharged out of the system
without passing through the drain piping.
The feed tank 19 of undiluted developing solution (e.g. 15 to 20 wt. %
aqueous solution of TMAH, concentrated aqueous solution of KOH) is
pressurized to, for example, 1 to 2 kgf/cm.sup.2 by N.sub.2 gas from the
piping 20, and the solution is fed under pressure as the undiluted
developing solution flow rate regulating valve 21 opens. The pure water is
supplied from a branch piping from the existing piping, and is fed as the
pure water flow regulating valve 22 opens. The undiluted developing
solution and pure water are fed as the individual valves are regulated
automatically, and are joined at the duct 23 and led to the duct 12,
thereby are entered into the development processing tank 1 as being mixed
with the circulating flow. It is also possible to supply the undiluted
developing solution and pure water directly into the duct 12 or
development processing tank 1 without joining on the way. It is, however,
desired to join the undiluted developing solution and pure water at the
duct 23 and then lead to the circulating duct 12 because they are mixed
sufficiently.
A sample solution is fed from the duct 14 into the electric conductivity
meter 15 and the absorption photometer 16 (for example, the two
instruments are combined in one body) installed online in the duct 10 for
the developing solution spray, and the electric conductivity and the
absorbance are measured continuously, and the measured solution is
returned to the duct 10 through the duct 17. It is also possible to
install the electric conductivity meter 15 and the absorption photometer
16 separately.
FIG. 2 is a schematic diagram of an apparatus showing other embodiment of
the invention. In the embodiment, instead of replenishing undiluted
developing solution and pure water by detecting the liquid level of the
developing solution by the liquid level gauge 3, as shown in FIG. 2, the
liquid level of the developing solution is detected by the liquid level
gauge 3, and a fresh developing solution preliminarily blending the
undiluted developing solution and pure water is replenished. Numeral 27 is
a feed tank for fresh developing solution, and 28 is a fresh solution flow
rate regulating valve. The other constitution is same as in FIG. 1.
FIG. 3 is a schematic diagram of an apparatus showing a different
embodiment of the invention. The embodiment is composed so as to detect
the dissolved resin concentration in the developing solution for resin by
the absorption photometer 16, and replenish undiluted developing solution
and pure water. As shown in FIG. 3, usually, the liquid level is near the
weir for overflow, and when undiluted developing solution or pure water is
replenished, the old developing solution overflows from the overflow weir,
and is discharged automatically. The discharge pump 18 is not necessarily
required, and a valve may be disposed in place of the discharge pump 18.
The other constitution is same as in FIG. 1.
FIG. 4 is a schematic diagram of an apparatus showing a further different
embodiment of the invention. The embodiment is desinged to replenish a
fresh developing solution preliminarily blending the undiluted developing
solution and pure water as shown in FIG. 4, instead of replenishing
undiluted developing solution and pure water in the third replenishing
means for replenishing by detecting the dissolved resin concentration in
the developing solution for resin by the absorption photometer 16. The
other constitution is same as in FIG. 3.
The control system of the apparatus in the embodiment in FIG. 1 is
explained. The liquid level gauge 3 and the liquid level in the
development processing tank 1, the electric conductivity meter 15 and the
alkali concentration of developing solution, and the absorption photometer
16 and the dissolved resin concentration in developing solution are
mutually independent functions in nature, but it is characteristic of the
invention to function them in mutually complementary relation.
Besides, in the first place, the target value of alkali concentration of
the developing solution and the deterioration limit value of the dissolved
resin concentration necessary for quality control of product boards must
be preset in the controllers on the basis of experience or calculation.
The alkali concentration of the developing solution declines due to
reaction with board resin, or absorption or reaction of carbon dioxide and
oxygen gas in air. As the alkali concentration declines, the line width
after development of the board resin changes to be thick (or narrow in
space), differing largely from the initial design value, which results in
phenomenon of poor dimensional precision. A practical example of operation
is shown in FIG. 5.
Therefore, the alkali concentration of the developing solution must be
controlled at a specified target value, for example, 2.38 (.+-.0.02) wt. %
in the case of TMAH. Conventionally, empirically, the degree of
deterioration of the developing solution was judged by the correlation
with the number of boards processed or chemical analysis or the like, but
prompt and accurate grasp was difficult.
The present inventor experimentally studied the relation between the alkali
concentration of developing solution and the electric conductivity, and
learned that the alkali concentration was predominant over the electric
conductivity near the concentration of use as shown in FIG. 6 so that it
could be measured with an advanced linear function.
The electric conductivity meter 15 installed online in the duct 10 has
compensating functions to minimize the measuring error and a conductivity
controller 25. The conductivity measurement of the sample solution led in
from the duct 10 is fed into the conductivity controller 25, and the
undiluted developing solution or pure water is automatically controlled by
the flow rate regulating valves 21, 22 by the output signal so as to
coincide with the target value, and replenished until the alkali
concentration is adjusted to the target value.
Deterioration of developing performance is also related with the dissolved
resin concentration, aside from the alkali concentration. The developing
solution processing the board is taken out from the development processing
tank 1 by the liquid feed pump 8, and is circulated through the developing
solution spray 7, and therefore the dissolved resin is gradually
concentrated in the developing solution. As a result, as shown in
operation example in FIG. 7, the residual film rate in the unexposed area
drops and the developing performance detriorates significantly, but
hitherto the concentration change was not measured in real time to control
the developing performance at a specific value. That is, the index of
deterioration was the number of boards processed, but since the board
shape, resin coating volume and the ratio between the exposed part and the
unexposed part are not constant, and the dissolved resin amount varies in
each type of board, and hence it is difficult to judge by the number of
boards processed.
The present inventor attempted to measure it in relation with the
absorbance from the studies on the resin contamination state of the
developing solution, and obtained the result as shown in FIG. 8 by
experiment. As shown in FIG. 8, the dissolved resin concentration and the
absorbance are in an advanced linear relation regardless of the alkali
concentration, and it is possible to judge the limit of the developing
performance by the dissolved resin concentration itself regardless of the
number of boards processed. Meanwhile, since the developing solution
becomes red due to dissolved resin, the measuring wavelength was 480 nm.
Therefore, the absorption photometer 16 installed in the duct 10 in one
body with or separately from the electric conductivity meter 15
continuously measures the dissolved resin concentration in the developing
solution, and when the value exceeding the deterioration limit is
detected, the discharge pump 18 is put in operation by the output signal
from the absorbance controller 26, and the deteriorating developing
solution is drawn out from the development processing tank 1, and is
discharged into the drain pipe, or directly discarded out of the system.
As a result, in the development processing tank 1 lowered in level, the
liquid level gauge 3 immediately detects the lowered liquid level, and a
fresh developing solution is replenished, and the dissolved resin
concentration is diluted to the deterioration limit value, so that the
developing performance is recovered, and the discharge pump 18 stops.
Here is stated the functional relation of the control system intended by
the apparatus in the embodiment in FIG. 1. When the development processing
tank 1 is empty and building up a solution, the liquid level gauge 3
detects the liquid level, and by the output signal from the liquid level
controller 24, the undiluted developing solution and pure water are
supplied, at a proper flow rate ratio, by regulating the valve opening
degree by means of flow rate regulating valves 21, 22.
In succession, the electric conductivity meter 15 continuously measures the
electric conductivity of the built-up developing solution, and by the
output signal from the conductivity controller 25, the undiluted
developing solution or pure water is supplied, at a proper small flow
rate, by regulating the valve opening degree by the flow rate regulating
valve 21 or 22 so as to be controlled automatically to achieve the alkali
concentration of the target value.
When the next development processing is started, lowering of alkali
concentration, drop of liquid level due to carry-over by boards, and
enrichment of dissolved resin are progressed.
When the alkali concentration is lowered, the electric conductivity of the
developing solution is continuously measured by the electric conductivity
meter 15, and by the output signal of the conductivity controller 25, the
undiluted developing solution is supplied at a proper small flow rate by
regulating the valve opening degree by the flow rate regulating valve 21
so as to be controlled automatically to maintain the alkali concentration
of the target value.
When the level of the solution drops as being brought out by the boards,
the liquid level gauge 3 detects the lowered liquid level, and by the
output signal of the liquid level controller 24, the undiluted developing
solution and pure water are supplied at a proper flow rate ratio by
regulating the valve opening degree by means of the flow rate regulating
valves 21, 22.
When the dissolved resin is concentrated to reach the deterioration limit,
the absorption photometer 16 detects the value exceeding the deterioration
limit by continuously measuring the dissolved resin concentration of the
developing solution, and by the output signal of the absorbance controller
26, the discharge pump 18 is put in action, and the deteriorating
developing solution is drawn out from the development processing tank 1,
and discarded into the drain pipe, or discarded directly out of the
system.
As a result, the liquid level drops, and the liquid level gauge 3 detects
the lowered liquid level, and by the output signal of the liquid level
controller 24, the undiluted developing solution and pure water are
supplied at a proper flow rate ratio by regulating the valve opening
degree by the flow rate regulating valves 21, 22. Since a fresh developing
solution is replenished, the developing performance is recovered as the
dissolved resin concentration is diluted to the deterioration limit, and
the discharge pump 18 stops.
Above the liquid level gauge 3, an overflow weir is disposed at a position
not allowing to overflow usually, but a slight overflow does not matter.
Next is described the functional relation of the control system intended by
the apparatus of the embodiment shown in FIG. 3. When the development
processing tank 1 is empty and building up a solution, by manual
operation, the undiluted developing solution and pure water are supplied
at a proper flow rate ratio by regulating the valve opening degree by the
flow rate regulating valves 21, 22.
The electric conductivity meter 15 continuously measures the electric
conductivity of the built-up developing solution, and by the output signal
of the conductivity controller 25, the undiluted developing solution or
pure water is supplied at a proper small flow rate by regulating the valve
opening degree by the flow rate regulating valve 21 or 22 so as to be
controlled automatically to reach the target of alkali concentration.
When next development process begins, lowering of alkali concentration,
drop of liquid level as brought out by boards, and enrichment of dissolved
resin are advanced.
In the case of lowering of alkali concentration, the electric conductivity
meter 15 continuously measures the electric conductivity of the developing
solution, and by the output signal of the conductivity controller 25, the
undiluted developing solution is supplied at a proper small flow rate by
regulating the valve opening degree by the flow rate regulating valve 21
so as to be controlled automatically to reach the target of alkali
concentration.
When the liquid level drops as being brought out by the boards, the liquid
level is slightly lower than the weir position for overflow.
When the dissolved resin is enriched to reach the deterioration limit, the
absorption photometer 16 continuously measures the dissolved resin
concentration in the developing solution, and when any value exceeding the
deterioration limit is detected, by the output of the absorbance
controller 26, the undiluted developing solution and pure water are
supplied at a proper flow rate ratio by regulating the valve opening
degree by the flow rate regulating valves 21, 22. Since a fresh developing
solution is replenished, the dissolved resin concentration is diluted to
the deterioration limit value, so that the developing performance is
recovered.
The liquid level is near the weir position for overflow, and when the
undiluted developing solution or pure water is replenished, the
deteriorating developing solution overflows from the overflow weir.
The present inventor, by applying the results on the basis of the control
functions in mutually complementary relations as described above, found by
experiment that the recovery of developing performance, continuous
operation, and saving of consumption of developing solution may be
realized easily and comprehensively.
Moreover, for conceptual understanding, the operation pattern effects are
compared between the invention and the prior art in FIGS. 9 to 12. In the
prior art, as shown in FIG. 10, the starting alkali concentration was, for
example, 2.38 wt. %, and the solution was exchanged when the concentration
was lowered to, for example, 2.29 wt. % in the course of time. In this
case, as shown in FIG. 10, the alkali concentration transition is in a
sawtooth profile, and due to variation width of the alkali concentration,
the developing performance was not constant.
By the apparatus of the invention, on the other hand, as shown in FIG. 9,
the alkali concentration remains constant at, for example, 2.38.+-.0.02
wt. % in the course of time, and it is not necessary to exchange the
solution, and the development performance is constant.
In the prior art, moreover, as shown in FIG. 12, the starting dissolved
resin concentration (at this time, the residual film rate in unexposed
area is, for example, 99%) increased as the time passed, and the solution
was exchanged when the concentration reached a specific value (at this
time, the residual film rate in unexposed area is, for example, 90%). In
this case, as shown in FIG. 12, the time course change of the dissolved
resin concentration is in a sawtooth profile, and variation width occurred
in the dissolved resin concentration, and hence the developing performance
was not stable.
According to the apparatus of the invention, by contrast, the dissolved
resin concentration remains constant after a certain time lapse as shown
in FIG. 11, and hence the residual film rate in unexposed area is
constant, not lowering, and it is not necessary to exchange the solution,
and the developing performance is constant.
Thus, having such constitution, the invention brings about the following
effects.
(1) By applying the invention in the liquid crystal board manufacturing
process or the printed board manufacturing process, the alkali
concentration and the dissolved resin concentration in the developing
solution are always monitored and controlled with the desired target
range, and continuous operation is possible for a long period at a stable
liquid level.
(2) Since the quality of the developing solution may be controlled
constant, the developing performance of board is stable, and when applied
in the liquid crystal board manufacturing process, comprehensive effects
are achieved, including a significant saving of consumption of solution,
decrese of down time, and reduction of labor and developing solution cost.
Having described preferred embodiments of the invention with reference to
the accompanying drawings, it is to be understood that the invention is
not limited to those precise embodiments, and that various changes and
modifications may be effected therein by one skilled in the art without
departing from the scope or spirit of the invention as defined in the
appended claims.
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